There are two potentially habitable planets orbiting Gilese 581

Remember Gliese 581g? The potentially habitable "second Earth" 20 light years away, also known as Zarmina? It's been looking dicey for a while, as many astronomers questioned its very existence.

But now, Gilese 581g has been re-added to the top five list of exoplanets considered prime candidates for harboring of life. New data from Steven Vogt of UC Santa Cruz clearly shows that it's quite real. And what's just as exciting is the realization that there are now two potentially habitable planets orbiting the same star.

Gilese 581g was originally discovered by astronomers of the Lick-Carnegie Exoplanet survey in 2010, but subsequent surveys were unable to detect it.

Full size The planet is about 1.5 times the size of Earth and it receives a similar amount of sunlight. Though it orbits a red dwarf, it resides within its sun's habitable zone and is considered the best exoplanetary candidate for life yet discovered.

As Abel Torres of Planetary Habitability Laboratory notes, "These factors combine to make Gliese 581g the most Earth-like planet known with an Earth Similarity Index, a measure of Earth-likeness from zero to one, of 0.92 and higher than the previously top candidate Gliese 667Cc, discovered last year."

And indeed, the Gilese system, with its two potentially life-friendly planets, may be our best bet when considering our first interstellar mission. At 20 light-years away, it's clearly the most exciting solar system in our immediate vicinity.

Other planets suspected of harboring life include Kepler-22b, HD85512, and Gliese 581d.